


Arresto Momentum

by 221butterbeer (Potterlocked)



Category: Harry Potter - J. K. Rowling, Sherlock (TV)
Genre: 221B Baker Street, Alternate Universe - Harry Potter Setting, Alternate Universe - Hogwarts, Big Brother Mycroft, Discovery, Johnlock - Freeform, M/M, Ministry of Magic, Post-Reichenbach, Potter!Lock, Potterlock, Reichenbach Falls, Reichenbach Fix-It, Reichenbach Theory, Wizard John
Language: English
Status: In-Progress
Published: 2015-09-08
Updated: 2015-09-23
Packaged: 2018-04-19 19:51:58
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 7
Words: 4,870
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/4758881
Author URL: https://archiveofourown.org/users/Potterlocked/pseuds/221butterbeer
Summary: <blockquote class="userstuff">
              <p>Potter!Lock – Harry Potter/ BBC Sherlock Xover. SH/JW. Sherlock shouldn't have survived the fall but John couldn't just let him die, even if it meant reminding him of the past life he left behind. After revealing to Sherlock the truth John had hidden since leaving his other world behind, the Consulting Detective must re-learn everything he thought he knew.</p>
            </blockquote>





	1. Falling Star

He was still alive. That was a surprise.

Sherlock had originally expected his fall to send him under for at least half an hour; had the truck been there to cushion his fall. He had realised the truck was driving away seconds after he succumbed to gravity but had nothing that he could do to stop it, all he could do was pray for a miracle. Of course he had many backup plans formulating in his mind, but it was too late and his previous backup plan had involved Mori— His thought trail ended, time seemed to slow down and, he felt as if he was stuck in an all-consuming vortex between time and reality for what seemed like forever before erratically dropping out of the euphoria onto the all too real, rock-hard ground below.  
The pain of colliding with the London pavement was near-blinding, but through his calculations, he had no idea why he was still alive. The carefully placed blood bags he and Molly had hidden just behind his hairline had burst open with the force of impact, and he could feel the blood smeared across his face and in his hair, dripping slowly down his neck onto the pavement below. Staring up to the heavens waiting for the mayhem to begin, he decided that although the stunt had gone wrong, the façade would still work if he went along with it as planned. Hopefully the all too realistic fall would be enough to fool those not in on the façade; especially John. He had to remember Molly telling him to relax, to keep his breathing slow and his eyes open no matter what. Despite the pain he was managing well, and being slumped on his side facing the bloodsplatted walls of St. Barts was making it easier.

The homeless network – some of the only few he can trust to do this – crowd forwards on cue, disguised as hospital visitors and professionals, a few as nurses and doctors, and a couple as paramedics waiting in the wings to rush forwards a few moments later. Keeping up the façade despite the pain he, sure enough, is proven correct when a couple of passing women (both office workers, mid-twenties and single, one looking for a promotion, one the boss of the other, both on the way to lunch) join the homeless network crowding around him.  
There is a prick in the skin on his right hand, rushed and hidden, judging by the slight shake of the needle hidden in one of the homeless network's hands. Through the pain, he can't feel it working, although he knows that any second he will – There. His hand is going numb, the agony of the rest of his body (four pulled muscles, two cracked ribs – one on either side, a dislocated ankle and left shoulder, a broken wrist and concussion) slowly subsiding thanks to the drugs. Sounds begin to slur, as the world starts to spin - the whole world slows down and speeds up all at once. He shoves the unwelcome feeling down, pushes everything away and prays his heartbeat slows enough in time. If anyone suspects, if John suspected…He couldn't bear thinking about.

He just lies there, staring, staring into nothing, as he waits for John to arrive; Limping most likely, due to the emotional stress causing his limp to re-emerge. Even with the drugs twisting at his mind Sherlock knows John is late. The stunt was carefully calculated, John should be here already. He had factored in the moments of shock, the time allowed for stumbling, being knocked down by the cyclist (Kevin, The youngest in the network but trustworthy enough, although he didn't know the whole plan) and getting back up again. He had worked it all out thirteen times, John should be here. If he's not here then, where is he? Did john get knocked down too hard? No, He told Kevin not to be too rough, that he only needed a few extra seconds to get into place. If it wasn't Kevin, No, The sniper. It could have been the sniper. What if Moriarty never intended to let them live anyway? He refuses to consider that fact that simply, John had left him. He knows better than that. John wouldn't have done that – Would he? He resists the urge to sit up and look around, to check if the façade worked; that John was alive. But he couldn't give himself away.  
The game was still on.


	2. Spelled Right?

 

John knew something was wrong before he even got the call. He didn't know why, but as an army doctor he had learnt to trust his instincts; and on this occasion, like many others, his gut instinct was right. As Sherlock's normally suave and pompous voice wavered John felt his stomach drop. Something was majorly wrong. Under Sherlock's strict instruction John turned slowly around to face St. Barts , staring blankly at the skyline before he noticed. A figure; silhouetted against the stark white of the building, with an all too familiar coat's collar turned up against the razor-sharp cheekbones John just knew were there. 'S-Sherlock?' John stuttered, barely managing to utter a sound through his clenched teeth, his body suddenly racked with an already all-consuming grief.

He was barely registering the words Sherlock was saying, utters of 'fake' and 'magic' were words that John couldn't and wouldn't associate with Sherlock. He couldn't register, he couldn't think straight and the only thing that his brain was able to formulate was a constant reminder that he had to do SOMETHING. Heck. The person he was closest to in the world was about to commit suicide and he couldn't do anything to stop him. Standing there, staring hopelessly at the great coat and cobalt blue scarf of his best friend flapping in the wind, he heard a faint 'Goodbye John' and the line dropped dead. 

Without thinking or caring about the secrecy surrounding what he was about to do John reached inside his coat pocket in a hasty struggle rummaging around for the token of his previous life that he couldn't quite bear to leave behind all together. He brushed against the smoothed oak with his fingertips feeling the familiar adrenaline that it brought begin to rush through his veins. Without a second thought he pulled what looked like a polished wooden 'stick' out from his pocket and pointed it at his best friend who was rapidly gaining terminal velocity. Yelling 'Arresto Momentum' at the top of his lungs, John prayed that in the split seconds previously he had used the right spell to slow Sherlock's fall.  
Sherlock never reached terminal velocity and slowed to almost a halt a few metres above the ground before falling the rest of the way at an unnaturally slowed speed. As blood spurted across Sherlock's face and a crowd of medical professionals surrounded him John turned away. He had failed. All he could do was wish he had never left his other world behind. He could have saved him. 

John had always wondered how Sherlock had never noticed the small amounts of magic he used around the flat but for the greatest detective in Europe, and most probably the world, Sherlock sure was unobservant to everyday occurrences. He hadn't quite grasped the fact that tea doesn't normally 'just make itself' whenever somebody wanted a cuppa and more biscuits flying out of the kitchen when they run out isn't quite normal. But John was thankful for these moments of Sherlock being oblivious to his magic; to be truthful, John missed his previous life, but after his injury he felt he needed a life without danger. Soon after leaving John realised he missed the action of his job with the ministry and was contemplating a return when he bumped into one of his old friends Mike Stamford, a squib who, like John, had taken a new life in London. Mike introduced him to Sherlock and the rest was history. The second John locked eyes on Sherlock he knew there was something different about him, that he would provide the spark of magic the mundane muggle world lacked, that he would become a welcomed and much loved alternative to the wizarding world and provide the adrenaline fix John missed all too much.

For what felt like forever John stood on the edge of the curb, staring at Sherlock's body and recalling all the other spells he could have used to save him (Goddammit John – Wingardium Leviosa!) when he noticed it.  
A faint twitch of Sherlock's left foot that only a man who had lived with the great Sherlock Holmes himself would happen to notice. His training had not failed him, but Sherlock was playing a damn good façade. He had to let Sherlock know that he was onto him but couldn't go over to the body in case he gave something away with the diminishing amount of grief he was displaying. Turning away from St. Barts he found the nearest security camera and stuck his middle fingers up to it. Within minutes a sleek black SUV pulled up beside him with the instruction to take him to Mycroft Holmes.


	3. Stray Genes

'John Watson you really are an unusual one aren't you? I do see why my brother keeps you around.' Mycroft Holmes drawled from the window of his office in the Diogenes Club. He turned around, his standard black umbrella swinging from his arm, and smiled at John as he entered the office. Mycroft Holmes took a seat in the deep red armchair behind his desk and indicated for John to take the seat opposite; John hesitantly sat down and stared across at Mycroft. 'You could have asked for me more civilly John, A simple nod to the camera would have done it.' Mycroft said exasperatedly, 'You really are an angry little hobbit aren't you?' A quickly suppressed grin broke across his face as John just shrugged his shoulders looking rather content with himself.

'So John, Is it me you wanted to talk to or do you wish for my nuisance brother to join us first?' Mycroft asked. He looked up, but in noting the look of surprise on John's face Mycroft reconsidered what he had previously said. With a scratch of his head, he found himself weirdly surprised at his brother. 'He didn't tell you?

Mycroft's question was met with a curt shake of John's head and the mouthing of the word 'bastard'. Mycroft couldn't help but be surprised at his brother's lack of communication with his best friend. Knowing that John would be distraught had Sherlock, in John's untold state, really committed suicide (Why do people care so much? – It really isn't an advantage.) Mycroft weighed up the possibilities as to how John knew. Luckily for Mycroft though, Sherlock burst through the door into Mycroft's office. 'Mycroft I'm going to ne-' He looked up and stopped; dead in his tracks.  
'John?' He uttered, looking solemnly at the man who was now up and limping towards him, gasping for an explanation. Sherlock tried for words, but nothing came; all he could do was mutter 'Not dead' before stalking over to Mycroft's desk, not being able to look John in the eye.

The tension in the room rose until Sherlock finally spoke, his normally fast and arrogant voice now slowed and uncertain; 'It went wrong' he said, sounding like a distressed child, 'But I survived. God dammit! How did I survive?' There was a slow intake of breath from Sherlock's side where John tried to suppress his anger and the fact that he knew exactly why Sherlock was alive. Mycroft could tell by John's expression that he was reluctant to tell Sherlock the truth any time soon. Mycroft looked across his desk at the pair of them, sat side by side in Mycroft's new tartan armchairs but still refusing to acknowledge each other's presence. Childish; the pair of them. In Mycroft's mind he had always been and always will be the clever one, but it hardly took a genius to realise that secretly they were grateful that the other was alive. Sherlock would take out his phone, pretending to text (There was no fooling him though, brother dear.) and steal glances to his left to check to see if John was bothered or not.

After a while Mycroft knew what needed to be done. He was tasked with telling Sherlock a very long time ago, but never quite had the heart to do so. He had known the second Sherlock met John that it could be a problem, that Sherlock could work out that things were not quite how they seemed. But Sherlock being Sherlock didn't seem to notice anything out of the norm and had probably deleted any glimpses of magic he saw from his mind straight away anyway, as he just didn't know that it wasn't another normal, mundane, thing that 'just happened'. Mycroft didn't want to subject his brother to the mind numbingly huge world he missed out on by just a few stray genes, but he couldn't leave him sulking over why he was alive forever, he deserved the truth, if not just to save his, and eventually John's sanity.


	4. Not just an Umbrella

Finally reclining back into his armchair, Mycroft gave an almost in-audible sigh whilst steepling his fingers beneath his chin in the standardly familiar Holmes manner. Reverting his gaze from the ceiling to the two men before him, Mycroft braced himself and sharply cleared his throat, drawing their attention. Mycroft grasped at the thousands of words floating around in his mind, not knowing where to start to explain to his brother what himself, his family and John were, how to explain what Sherlock had missed out on and what Sherlock's life could have been.  
Mycroft felt his brother's ice-cold blue eyes boring into his back as he turned to the side in his chair and picked up his umbrella from its usual place, propped up near to his person at all times, just in case. Wordlessly Mycroft set the umbrella on the desk before him, clearing away papers to create a proper space for it. John and Sherlock looked at him strangely, but as Mycroft twisted the handle away from the umbrella their faces became a picture of confused awe as he revealed just why Mycroft was never seen without his infamous umbrella.

The handle of the umbrella fully pulled away, leaving a polished black stick in its wake; the grip of the stick forming the umbrella's distinctive handle. Mycroft set it down on the desk, and John and Sherlock both craned to look at it; it was a deep mahogany and highly shined, with a carved wooden handle which curved round to form the previous umbrella handle. This handle was also a deep woody colour, but had small silver edgings, forming a family crest and emblem which looked centuries old. Mycroft broke the silence.   
"12 1/4 inches, ebony, dragon heartstring, 12 generations of Holmes' old" Mycroft simply stated. John audibly gasped whilst Sherlock just spluttered in response. 

"What the HELL is that" Sherlock managed to spit out, mind racing to find his own plausible explanation of the implausible object on the desk in front of him. The only response he got was Mycroft reaching out and picking up the wand (wand?!) on the desk before him and giving it a sharp flick.

Everything Sherlock thought he knew about chemistry, physics and how the world worked dropped into oblivion as the entire room around him began to swim, as if they were being pushed through a portal; the ceiling heightened, the room expanded and nothing made sense any longer. Gone were the mundane London street maps that adorned the walls and the patriotic portrait of the Queen that loomed high above Mycroft's desk, leaving in their wake paintings that covered almost every surface on the walls, in which, Sherlock was amazed to see, the subjects appeared to be moving and conversing (?!) with one another.  
The sleek black minimalist office that the reunion party had once been sitting in had vanished before Sherlock's eyes, leaving a mind bogglingly large office in it's place with almost every surface covered with something; whether it be strange golden machines and trinkets, stacks upon stacks of books and strangely, Sherlock noted, not a single electronic object in sight. To his right sat a strangely un-phased John Watson, whereas to his right there was now a large red and gold (vulture?) perched on an ornate bird stand singing the most beautiful song he had ever heard. Sherlock stored the tune in his mind palace under: "To translate into violin masterpieces" as he thought about just how much Mrs. Hudson would love it. 


	5. The Anomaly

Mycroft watched with a sad satisfaction whilst his brother's face contorted into a picture of confused awe as his humdrum life dropped away at his feet and he was faced with an entire new world he knew nothing about. Everything that had made Sherlock "special" or a "genius" in the muggle world was different here, here he was like the everyday Londoners, the boring people, those who see and do not observe; and he was clueless.   
Knowing that just lifting the glamour spell on the office wouldn't serve as an explanation to his little brother, Mycroft was forced to lay down his hand.   
"Sherlock?" he began hesitantly, but he got no response from the man, whose icy blue eyes were staring straight at him, as if they were looking right into his soul. "Sherlock?" Minutes upon minutes past with not a single movement or indication of a response from Sherlock.  
"Okay Sherlock that's getting a little bit scary now" John's voice rang out from beside his brother after what must have been 5 minutes, and only at the sound of the doctor's voice did Sherlock drop out of his trance-like state, looking with a confused air at the shorter man beside him. 

"What's getting scary?" Sherlock asked him, for he was secretly rather proud of the speech he had just launched into, explaining how when you have eliminated the impossible, whatever remains, however improbable, must be the truth. How in this case, for the first time, he did not understand the truth, how there is no science or reason to what he had just witnessed but under the circumstances he had concluded that the only explanation was magic.   
After a fleeting look of annoyance that passed over Mycroft's face and a sigh from John beside him, regrettably it transpired to Sherlock that he had not in fact said any of this speech aloud. This episode is what spurred Mycroft to finally find it within himself to disclose everything he should have disclosed all those years ago. Despite the fact they argued about almost everything and claimed they were 'arch enemies', the brothers truly did care for one another and Mycroft hated seeing Sherlock like this, even more like a machine than normal, his genius reduced to confusion.

"Sherlock," he simply stated, not knowing how else to start, "I am a wizard."

For the first time in a long time Mycroft couldn't read his brother; it was as if every emotion was passing through Sherlock's suposedly unfeeling brain, and was leaving a patchwork trail of everything and nothing across his face. It was confused but in awe, sad but amazed, angry but calculated and it terrified Mycroft. Knowing he couldn't stop now he tried to ignore his brother's immovable gaze and continued. "I have the ability to wield magic, and as do our mother, father, grandparents and just about everyone else you have ever met in the extended Holmes family. We are part of an ancient pureblood family, and rival only the Malfoy's in status and age. We Holmes' can be traced back through centuries of magic right back to being Slazaar Slytherin's right hand man at the dawn of the magical revolution." Mycroft looked across to his brother with a glaze of sadness over his eyes. Knowing there was no way to soften the blow, Mycroft put it bluntly.  
"All of us except for you Sherlock. You were the anomaly, and as much as all of us willed it, you never showed any signs of magic, no accidental blowings up of the bathroom, no changing the colour of your room at will, no toys floating towards you from across the room – nothing. Brother dear, it pains me to tell you, but you are a squib." 


	6. Hogwarts is for Un-learning

John, who had remained decidedly silent during this exchange so far, let out a small gasp at finding out his flatmate was a squib.

When John escaped from the wizarding world after his injury and retreated into the muggle suburbia which was London, he had tried to run away from anything remotely magic that could draw him back. As soon as John met Sherlock he knew that he was the perfect muggle he could flat share with since he was so, to think of a kinder word, abnormal. Abnormal in the fact that he captivated John and allowed him to not crave the adrenaline fuelled adventure of being an Auror with the ministry. Abnormal in the way that he was so mind bogglingly intelligent but so so ignorant. Abnormal in the fact that John Watson no longer missed the wizarding world because he had his own share of the magic that was Sherlock Holmes every single day at 221b Baker Street.

But this perfect slice of abnormality to match John's didn't last for long.

John Watson did not need introducing to Mycroft Holmes when he was essentially kidnapped by him after Mycroft found out about John and Sherlock's flat share. He already knew exactly who Mycroft was. Everything John had tried to run from, everything new he had built for himself crumbled as the Minister of Magic stood before him and introduced himself as Sherlock's elder brother. Of all the people in London he could have chosen to flat share with, John Watson had managed to select none other than the Minister of Magic's younger brother; quite possibly the only other person in London with the magical ties he was trying so hard to escape from. This only lead to one question though; why was the illusive Sherlock Holmes in London?

Of course deep down John had known the answer.

But John Hamish Watson was the child of a very traditional Scottish pure-blood wizard and a gentle English half-blood witch. Growing up John found himself subject to the strong beliefs of his father, which his mother, being the gentle soul she was, never rebutted. He was taught from a young age to look down on muggles, house-elves, blood traitors and 'mudbloods' but below even that were the, in his father's eyes, disgraced squibs.   
Learning this hatred early on is as much damaging to the child as it is to any relationships they consequently try to form in the future; but it was his mother who kept him from becoming the pure-blood supremacist that his father was training him to become and allowed him to form healthy friendships and keep his sanity. His mother, being a half-blood, taught him about the muggle world and he was instantly captivated by the way they combated daily life without magic. He loved everything about the science and reason of muggle life and spent all his spare time in the Hogwarts library studying the muggle world until he understood it as if it were his own. 

Throughout John's time at Hogwarts he had learnt many things, and excelled in all his classes, but by far the hardest thing of all was un-learning everything his father had drilled into him about blood status and magical capabilities during his childhood, despite how much he disagreed with the opinions in question. As much as he tried he would still occasionally make remarks or think things that he instantly realised were wrong in the ever-changing magical community and feel absolutely awful.   
The fact that Sherlock was a squib should not affect John in any way and should not imply that Sherlock was below anyone for any reason whatsoever, but, despite this, John still felt the slightest bit conflicted about how to approach the matter due to the influence of his father; so had instead of thinking too hard about it, decided to ignore the fact that Sherlock was a squib altogether and focus more on un-learning the prejudiced opinions he had inherited and form his own accepting ones instead.


	7. So wrong it's right

Upon hearing this news it was as if John and Sherlock's emotional ranges had swapped completely. John seemed close to emotionless, whereas Sherlock was in emotional turmoil. His brain was a well-trained machine, but now it seemed that it was malfunctioning. Nothing made sense and he could feel everything.   
All the emotions he had suppressed for so long took their chances and resurfaced, leaving him an absolute wreck. Confused and dazed Sherlock looked bewilderedly around Mycroft's gleaming office and was mesmerised by its contrast to anything he had ever seen before.

As his eyes flitted over Mycroft's desk, his gaze fell onto an ornately framed picture of himself and his brother as infants. As he looked at the picture it seemed to reawaken an entire lost chapter of his life; memories began to flood back to him. The things he could remember from his childhood that he had hidden away in the back of his mind palace as illogical and impossible childhood whims suddenly now made sense.   
Like the time Redbeard (oh Redbeard!) had suddenly floated across the living room and nobody had even batted an eyelid. The time that Nana Holmes' perfectly permed hair had changed from blonde to baby blue to candy floss pink and back again consistently throughout the Holmes family Christmas dinner. And most poignantly of all, the time Mycroft had returned home from a shopping trip to London with Mummy and Daddy and returned with an array of strange looking objects, the strangest being some sort of carved and polished stick that spat coloured sparks out of the end when Mycroft waved it but did nothing when Sherlock waved it, however hard he tried. Sherlock could remember the tears in his eyes at his anguish and moments later Mummy Holmes scooping him up in her arms, brushing his curls out of his eyes and smiling sadly at him.  
'Sherlock, darling, don't cry' she said, 'I know in here', she pointed a beautifully manicured finger to her chest over her heart whilst he wiped his tears away, 'That you'll do brilliant things, things we Holmes' could never imagine, but maybe, just maybe, this just isn't for you.' 

Everything about this secret wizarding world he could now remember was so wrong that it was right. Somehow Sherlock could see how it worked and fitted into the muggle world around him as well as the wizarding world, filling in the gaps in knowledge and logic that he had never managed to find answers to. The more he remembered of his childhood the more the magic made sense.

Thinking back to his younger years, he remembered the case of Godric's Hollow, in which 12 people died suddenly on the side of the sleepy town's main street with no obvious reasons as to why. As a young amateur detective at the time, and desperate to prove himself to his ever absent elder brother, Sherlock had been determined to solve the mysterious crime but had never managed it; there were no traces of anything out of the norm in the bodies, which were all in perfect health and had nothing internally wrong, no signs of trauma to the body externally at all and there was not even a single drop of blood in sight. Eventually after much struggling and nicotine patches Sherlock had to give in and the West Country police force put the deaths down to 12 simultaneous heart attacks and quickly closed the case without any further questions to avoid a media storm and mass panic. That case had remained the case that had bothered Sherlock the most. The one that didn't make any sense or stand to reason; but now he had a new possibility to the cause of death – endless new possibilities and he would bet his entire secret stash of cigarettes in the 221b that these 12 people were killed by magic of some way, shape or form.

Sherlock wanted to be sad that he didn't have magic, and that he had missed out on this entire magical world, and deep down inside he was, but now he had the best of both worlds; two lives and boy was he going to take hold of that with both hands! He had so many new opportunities and now Sherlock, thinking rationally in this completely un-rational situation, realised he had better take advantage of them now to make up for lost time, for now he was not just the only Consulting Detective in the world (he'd invented the job) but also now the only muggle with such magical connections to use in this pivotal invented detective role; he had so many opportunities and nowhere near enough time to grasp and exploit them all.

He needed to think.

**Author's Note:**

> This fic was originally published on FF.net; my username there is 221butterbeer :)


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